The present invention relates to a joint structure for a golf club, and more particularly relates to improvement in joint strength between a hosel and a shaft of a golf club.
In a conventional construction of a metallic golf club, a shaft made of FRP is inserted into and bonded to a hosel of the golf club. In order to enhance the joint strength between the shaft and the hosel, use of a reinforcement called "ferrule" has already been proposed in, for example, Japanese Utility Model Opening Sho. 64-54574.
Such a ferrule is a monolithic element made up of a conical sleeve section and a cylindrical barrel section and a cylindrical hole is formed longitudinally through the two sections. The cylindrical hole is adapted for accommodating a shaft.
In assemblage of a golf club, the cylindrical barrel section of the ferrule is first inserted into an enlarged upper end section of a shaft hole formed in the hosel and a tip of the shaft is inserted into the shaft hole past the cylindrical hole in the ferrule. By application of bonding agent, the tip of the shaft is fixed to the ferrule and the hosel by assistance of an intermediate bond layer. Presence of the cylindrical barrel section in the joint region well mitigates stress concentration on the mating plane between the ferrule and the hosel at shooting balls.
With this construction of the conventional ferrule, however, a relatively smooth surface of the barrel section tends to allow accidental separation of the ferrule from the hosel when impulsive stress at shooting balls acts on the joint structure repeatedly.